The present invention relates in general to methods of making pressurized balls and more particularly to an improved, faster method of making a two part core for tennis balls, or the like, where the core halves are thermally bonded to one another.
The conventional, presently used methods of manufacturing pressurized ball cores, such as for tennis balls, is to bond two semi-hemispheric ball halves by pressing together the cemented edges of the two halves in a pressurized environment. When making tennis balls, such pressurized environment is approximately 18 psi above atmospheric pressure at sea level. Subsequently, when the thermosetting adhesive or cement is cured through the use of heat, the captured air mass within the ball causes the internal ball pressure to increase greatly, this is particularly true where curing temperatures are in excess of 300.degree. F. Such captured internal air mass and the resultant pressure occasioned by the curing temperatures increases the time for requiring the associated mold to be maintained in a closed position since it is necessary to not only allow the associated cement or adhesive to be cooled, and thus set the adhesive with the core halves bonded together, but also to allow cooling of the captured air mass so that the internal pressures will be reduced to a level which will not blow the two core halves apart. Therefore, conventional methods now used require that the bonding mold and the ball core be cooled down sufficiently to lower the temperature of the core and the air inside to create a pressure value that will not blow the ball apart.
It is also common in present methods of making pressurized ball cores to have the partible mold used for pressuring and heating the core halves together have an intimate complete surface to surface contact to withstand the high internal pressures occasioned by the heating of the captured elevated air pressure within the core.